Data communication in a computer network involves the exchange of data between two or more entities interconnected by communication links. Generally, the functions associated with the various communicating entities and the network itself are fixed; that is, entry of an entity into the network does not affect the functioning of the network, or of the entities themselves. While this model is well-suited to traditional processing environments where computational roles remain unchanged and the network is intended merely to facilitate resource sharing and communication, it limits the user relevance of computers to applications--such as word processing, spreadsheet, and database systems--involving the performance of routine tasks.
Indeed, the idea of a single individual operating a single station on a computer network by its very nature limits the uses to which computers may be put, as well as the relationship between computers and their users. The user's interaction with the computer is typically limited to information exchanged on a video screen. Even interfaces that allow the user to enter commands and data through action, rather than by keystroke, expand the degree of interaction only marginally. For example, interface devices such as the mouse and the joystick follow a "marionette" model, mimicking on-screen the gestures of a user. Interaction with the computer is therefore limited by the need for physical dexterity in manipulating the input device, as well as by the limited responses offered by the computer itself. Accordingly, while such interface devices may vary the mode of interaction, its scope remains essentially unchanged: output is confined to the screen, and input arises from highly constrained user gestural patterns.
To extend the capabilities of computers beyond the screen and into users' lives, proposals have been made for "augmented objects," such as coffee cups and stuffed animals that afford an entirely different approach to user-computer interaction. These devices, of course, have their own inherent limitations based on the modes in which the user would normally interact with the (unaugmented) object.